The Global Positioning System (GPS) has long been employed by the military to accurately determine the position of any given person or object around the globe. In the civilian arena, GPS-based applications have also proliferated. GPS positioning has been employed for purposes as diverse as navigation, farming, telecommunication, location-based marketing and advertising, etc.
GPS circuitry can now be found in many consumer devices. In a typical GPS navigation device, for example, a GPS receiver circuit receives GPS signals from a set of GPS satellites. The GPS receiver circuitry determines its own position from the received GPS signals, and can also determine the required course and speed to navigate to other locations if desired. GPS circuitry is also found in mobile telecommunication devices, such as cellular mobile handsets. By offering position-based functionalities (such as navigation, location-based searching, marketing, advertising, etc.), manufacturers and network operators entice telecommunication consumers with an increasing array of sophisticated features and services, thereby enhancing profitability and/or user satisfaction.
GPS-equipped cellular phones have certain particular requirements that manufacturers strive to satisfy. Generally speaking, the GPS circuitry in a typical cellular phone needs to be inexpensive, relatively small in form factor and sufficiently rugged to integrate with a typical consumer's mobile handset, and to consume a relatively low amount of power to extend the battery life of the typical mobile handset. Furthermore, the GPS circuitry in a typical cellular phone needs to have a rapid position acquisition capability to satisfy a technically unsophisticated but demanding and fickle consumer base. Thus, while a trained pilot may be satisfied with a thirty-second GPS cold start at the beginning of a multi-hour flight (i.e., the GPS receiver takes 30 seconds to fix its position), a typical consumer loses interest if the position-based application in his cell phone is not available instantly or within a short time after he turns on his cellular phone or after he moves to a given location.
To satisfy the particular demands of the consumer market, GPS positioning in cellular handsets has long been accomplished with the assistance of a cellular network. For example, in order to minimize the delay in acquiring the GPS position and/or to assist a cellular handset in acquiring its GPS position in a difficult RF environment, the cellular network typically provides “aiding hints” to the GPS circuitry in the cellular handset to allow the GPS circuitry to more quickly fix its GPS position.
To facilitate discussion, FIG. 1 illustrates a simplified CDMA (Code Division Multiple Access) network 100 having a plurality of cellular transmission towers 102, 104, and 106. For signal transmission management purposes, the spatial region in the vicinity of each cellular tower tends to be divided into a plurality of sectors. A given cellular phone may be assigned to a particular sector of a particular cellular transmission tower for communication purposes. In the example of FIG. 1 tower 102 is shown with sectors 102a, 102b, and 102c; tower 104 is shown with sectors 104a, 104b, and 104c; and tower 106 is shown with sectors 106a, 106b, and 106c. The towers themselves tend to be connected using high-speed transmission optical, wired, or wireless links, which may utilize a protocol such as SS7 for communication purposes. These communication links are shown as communication links 120, 122, and 124 in FIG. 1.
A CDMA network switch 128, representing for example a MSC switch, is also shown. A CDMA Positioning Determining Entity (PDE) 130 is shown coupled to CDMA network switch 128. CDMA PDE 130 represents the network logic that enables the GPS positioning capability in the CDMA mobile handsets (such as CDMA MS 112). CDMA PDE 130 communicates with the CDMA mobile handsets to offer GPS position-based functionalities while these CDMA mobile handsets are within CDMA network 100.
Generally speaking, CDMA PDE 130 works cooperatively with CDMA network 100 and CDMA MS 112 and relies on certain CDMA-specific features and information provided by CDMA network 100 and CDMA MS 112 to generate aiding hints and to provide these aiding hints to CDMA MS 112. The aiding hints enable CDMA MS 112 to more quickly and/or more efficiently acquire the requisite GPS signals from the GPS satellites (such as GPS satellites 140, 142, and 144 of FIG. 1). Once CDMA MS 112 acquires the requisite GPS signals with the assistance of the PDE-provided aiding hints, CDMA PDE 130 may assist CDMA MS 112 in resolving these GPS signals (taking into account network-specific and circuit-specific delays and offsets) into useful GPS information, such as the exact GPS position of CDMA MS 112.
To facilitate discussion, FIG. 2 illustrates a simplified GPS position acquisition process for a typical CDMA mobile handset, such as CDMA MS 112 of FIG. 1, while the CDMA mobile handset is within the CDMA network. The GPS position acquisition process begins with the establishment of a session (202) between CDMA MS 112 and CDMA PDE 130 via the transmission facilities (e.g., towers and switches) of CDMA network 100. Generically speaking, the GPS session may be thought of as a call between CDMA MS 112 and CDMA PDE 130 for information exchange purposes.
In step 204, CDMA PDE 130 requests information (such as certain sector-related identification and timing information) from CDMA MS 112 for AFLT (Advanced Forward Link Trilateration) purposes. In step 206, CDMA MS 112 furnishes the requested information, such as the sector-related information for the transmission towers sectors that CDMA MS 112 detects. The furnished information is employed (210) by CDMA PDE 130 to compute (e.g., triangulate in step 208) the rough location of CDMA MS 112 in CDMA network 100.
In step 212, CDMA PDE 130 sends aiding data, which is based on the calculated AFLT position, to CDMA MS 112 to enable CDMA MS 112 to more quickly obtain its GPS signals. For example, CDMA PDE 130 may send the identifying data pertaining to the subset of GPS satellites that CDMA MS 112 most likely will be able to lock on based on the calculated AFLT position, GPS timing estimates, GPS Doppler estimates, etc. This aiding information reduces the searching effort that CDMA MS 112 needs to perform to acquire the requisite GPS signals.
For example, CDMA MS 112 may direct the search only to the GPS satellites identified in the aiding information and may skip all other GPS satellites not identified in the aiding information. As another example, CDMA MS 112 may employ the GPS timing data and GPS Doppler data in the aiding information to more efficiently synchronize itself for GPS signal acquisition purposes.
In step 214, CDMA MS 112 may return raw GPS signal data (if found) to CDMA PDE 130. Since CDMA PDE 130 is not as severely constrained in terms of form factor and/or power usage requirement, there may be more processing capability within CDMA PDE 130 (compared to the processing capability in CDMA MS 112) to more quickly calculate the GPS position from the returned raw GPS signal data. Once the GPS position of CDMA MS 112 is determined, GPS position-based applications and features may become available to the user of CDMA MS 112 while CDMA MS 112 is inside CDMA network 100.
While the aforementioned GPS position acquisition process tends to work adequately for cellular mobile handsets, there are drawbacks. For example, CDMA PDE is highly specific to the RF, electrical, physical layout, and protocol characteristics of CDMA network 100. This is because CDMA PDE needs to account for chip-related delays, physical transmission delays due to specific component layout, protocol-related issues, network functions, and other particularities of CDMA network 100 to be able to compensate for these particularities and to provide reasonably accurate GPS and timing hints to CDMA MS 112.
Likewise, the AFLT position calculation process in the CDMA PDE 130 that employs the MS-furnished CDMA sector data to calculate the rough position of CDMA MS 112 is highly specific to, for example, the network tower locations and transmission characteristics of a particular CDMA network, as well as on the specific data and timing format and requirements of the CDMA protocol. While the tight coupling between the GPS position acquisition process and the CDMA network/protocol presents little difficulty for CDMA cellular mobile handsets within a CDMA network, such tight coupling also implies that these CDMA cellular mobile handsets lose some or all of their GPS functionalities and features when traveling outside of the reach of the CDMA network and its CDMA-specific PDE.
Nowadays, there exists a new class of cellular mobile devices that can interoperate across networks and protocols. For example, some multi-mode cellular mobile handsets are designed to operate across CDMA, WiFi, and/or WiMax networks. Since the GPS functionality is dependent on the existence of the CDMA network and/or the CDMA PDE and its knowledge of the specific CDMA network and protocol, users of such multi-mode cellular mobile handsets may be unable to access GPS position-based functionalities while roaming outside of the CDMA network into a WiFi network or a WiMax network.
In these cases, such a user may notice that he may make and receive calls in a non-CDMA network but may otherwise be unable to use his GPS position-based features and/or be able to obtain a quick GPS position fix due to the lack of CDMA network aiding information. Such failures may lead the user to believe that his cellular phone or the network has somehow malfunctioned, and may result in user frustration and dissatisfaction. If the user is sufficiently dissatisfied, the user may cancel the GPS feature altogether, resulting in a loss of revenue for the network operator.